1. Field of the Invention
The present invention relates to a sheet processing device and an image forming apparatus.
2. Description of the Related Art
Heretofore, as a sheet processing device that implements predetermined processing such as binding and punching for a plurality of superimposed sheets, for example, a sheet processing device described in Japanese Patent Laid-Open Publication No. H10-139256 has been known. Such a sheet processing device includes: a reservoir unit for stacking and superimposing the sheets before being subjected to the predetermined processing, and for determining a position of the sheets with respect to a sheet processing unit that implements the predetermined processing therefor; and a discharge unit for discharging the sheets, which are subjected to the predetermined processing, from the reservoir unit.
Incidentally, in the case of performing the predetermined processing plurality of times continuously, if the sheets already subjected to the predetermined processing remain in the reservoir unit for a long time, then sheets to be subjected to the predetermined processing next cannot be reserved in the reservoir unit, and productivity is lowered. Hence, the discharge unit is required to promptly discharge the sheets already subjected to the predetermined processing. Specifically, there is performed an operation of increasing a rotation speed of a motor that operates the discharge unit when the discharge unit performs an operation for discharging the sheets.
However, when the rotation speed of the motor is increased, torque of the motor is decreased. Meanwhile, a load is applied to the motor owing to weight of the plurality of sheets subjected to the predetermined processing. Therefore, when the rotation speed of the motor is simply increased for the purpose of increasing such a discharge speed, an overload is sometimes applied to the motor.
In particular, in the discharge of the sheets, a stepping motor is used for control such as positioning of a delivery hook that engages and discharges the sheets, and accordingly, the stepping motor sometimes causes a loss of synchronization by the fact that the overload is applied thereto. Although a possibility of the loss of synchronization is reduced by using a large motor with large torque, the large motor is expensive, and use of the large motor also causes a size increase of the apparatus.